Constraints On Dark Matter And Milky Way Satellite Galaxies From Cosmological Simulations

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Constraints on Dark Matter and Milky Way Satellite Galaxies from Cosmological Simulations

Author : Miguel Eduardo Rocha Gaso
Publisher :
ISBN 13 : 9781303810305
Total Pages : 181 pages
Book Rating : 4.8/5 (13 download)

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Book Synopsis Constraints on Dark Matter and Milky Way Satellite Galaxies from Cosmological Simulations by : Miguel Eduardo Rocha Gaso

Download or read book Constraints on Dark Matter and Milky Way Satellite Galaxies from Cosmological Simulations written by Miguel Eduardo Rocha Gaso and published by . This book was released on 2014 with total page 181 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cosmological simulations describing the non-linear evolution of dark matter structures in the Universe have become an indispensable tool to study the predictions made by our standard model of cosmology, and to confront them with observations. In this thesis I present a new idea for using cosmological simulations to infer the accretion times of Milky Way satellite galaxies from their observed positions and kinematics. We find that Carina, Ursa Minor, and Sculptor were all accreted early, more than 8 Gyr ago. Five other dwarfs, including Sextans and Segue 1, are also probable early accreters, though with larger uncertainties. On the other extreme, Leo T is just falling into the Milky Way for the first time while Leo I fell ~2 Gyr ago and is now climbing out of the Milky Way's potential after its first perigalacticon. The energies of several other dwarfs, including Fornax and Hercules, point to intermediate infall times, 2 - 8 Gyr ago. Our analysis suggests that the Large Magellanic Cloud crossed inside the Milky Way virial radius recently, within the last ~4 billion years. Also I present new constrains on how strongly dark matter particles can interact with themselves. For this we use a set cosmological simulations that implement a new self-consistent algorithm to treat dark matter self-interactions. We find that self-interacting dark matter models with cross sections in the order [sigma]/m ~ 0.5 cm2 /g ~ 1 barn/GeV would be capable of reproducing the observed core sizes and central densities of dark matter halos in a wide range of scales, from tiny dwarf galaxies to large galaxy clusters, without violating any other observational constraints. Higher resolution simulations over a wider range of masses and properly accounting for the effects of baryonic processes that are not yet included in our simulation will be required to confirm our expectations and place better constraints. I discuss our plans for achieving this goal and show some preliminary results from a new set of simulations.

Dark Matter Constraints from Observations of 25 Milky Way Satellite Galaxies with the Fermi Large Area Telescope

Author :
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (965 download)

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Book Synopsis Dark Matter Constraints from Observations of 25 Milky Way Satellite Galaxies with the Fermi Large Area Telescope by :

Download or read book Dark Matter Constraints from Observations of 25 Milky Way Satellite Galaxies with the Fermi Large Area Telescope written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The dwarf spheroidal satellite galaxies of the Milky Way are some of the most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack of astrophysical backgrounds, dwarf spheroidal galaxies are widely considered to be among the most promising targets for the indirect detection of dark matter via gamma rays. Here we report on gamma-ray observations of 25 Milky Way dwarf spheroidal satellite galaxies based on 4 years of Fermi Large Area Telescope (LAT) data. None of the dwarf galaxies are significantly detected in gamma rays, and we present gamma-ray flux upper limits between 500 MeV and 500 GeV. We determine the dark matter content of 18 dwarf spheroidal galaxies from stellar kinematic data and combine LAT observations of 15 dwarf galaxies to constrain the dark matter annihilation cross section. We set some of the tightest constraints to date on the the annihilation of dark matter particles with masses between 2 GeV and 10 TeV into prototypical Standard Model channels. We find these results to be robust against systematic uncertainties in the LAT instrument performance, diffuse gamma-ray background modeling, and assumed dark matter density profile.

Faint Galaxies and Small Halos

Author : Ethan Oliver Nadler
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (125 download)

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Book Synopsis Faint Galaxies and Small Halos by : Ethan Oliver Nadler

Download or read book Faint Galaxies and Small Halos written by Ethan Oliver Nadler and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis addresses the intersection of dark matter and galaxy formation physics by modeling the faintest galaxies in the Universe in a cosmological context. In the first part of this work, I present an empirical model for the connection between faint galaxies and small dark matter halos. Combining this model with tailored cosmological simulations of Milky Way analogs and state-of-the-art satellite galaxy observations yields new insights into dwarf galaxy formation and hierarchical structure formation. Next, I show that these same dwarf galaxy observations place stringent constraints on microphysical dark matter properties including its warmth, self-interactions, Standard Model interactions, minimum particle mass, and formation epoch. Finally, I describe a unified framework that combines dark matter constraints from dwarf galaxies and strong gravitational lensing, paving the way for next-generation surveys of small-scale cosmic structure to deliver unprecedented insights into dark matter physics.

Testing Galaxy Formation and the Nature of Dark Matter with Satellite Galaxies

Author : Anna Mercedes Nierenberg
Publisher :
ISBN 13 : 9781321349894
Total Pages : 218 pages
Book Rating : 4.3/5 (498 download)

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Book Synopsis Testing Galaxy Formation and the Nature of Dark Matter with Satellite Galaxies by : Anna Mercedes Nierenberg

Download or read book Testing Galaxy Formation and the Nature of Dark Matter with Satellite Galaxies written by Anna Mercedes Nierenberg and published by . This book was released on 2014 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: The abundance of low mass halos is one of the key predictions of LCDM, which remains at apparent odds with observations of luminous structure. We present new measurements of the spatial distribution and the cumulative luminosity function of satellite galaxies up to a thousand times fainter than their hosts, as a function of host stellar mass and morphology between redshifts 0.1 and 0.8, using imaging from the GOODS and COSMOS fields in conjunction with a rigorous statistical analysis. We demonstrate how these measurements provide powerful new constraints for abundance matching and cosmological simulations in the context of both warm and cold dark matter, and how future measurements of faint satellite colors using CANDELS, will provide important distinguishing power between warm and cold dark matter models. In addition, we present results from a complementary gravitational lens modeling project in which we use strongly lensed AGN narrow-line emission in order to detect dark matter subhalos, demonstrating a promising new method for measuring the subhalo mass function in thousands of lensed systems which will be discovered in ongoing and future optical surveys.

Precision Cosmology with Galaxy Cluster Surveys

Author : Hao-Yi Wu
Publisher : Stanford University
ISBN 13 :
Total Pages : 234 pages
Book Rating : 4.F/5 ( download)

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Book Synopsis Precision Cosmology with Galaxy Cluster Surveys by : Hao-Yi Wu

Download or read book Precision Cosmology with Galaxy Cluster Surveys written by Hao-Yi Wu and published by Stanford University. This book was released on 2011 with total page 234 pages. Available in PDF, EPUB and Kindle. Book excerpt: The acceleration of the universe, which is often attributed to "dark energy, " has posed one of the main challenges to fundamental physics. Galaxy clusters provide one of the most sensitive probes of dark energy because their abundance reflects the growth rate of large-scale structure and the expansion rate of the universe. Several large galaxy cluster surveys will soon provide tremendous statistical power to constrain the properties of dark energy; however, the constraining power of these surveys will be determined by how well systematic errors are controlled. Of these systematic errors, the dominant one comes from inferring cluster masses using observable signals of clusters, the so-called "observable--mass distribution." This thesis focuses on extracting dark energy information from forthcoming large galaxy cluster surveys, including how we maximize the cosmological information, how we control important systematics, and how precisely we need to calibrate theoretical models. We study how multi-wavelength follow-up observations can improve cluster mass calibration in optical surveys. We also investigate the impact of theoretical uncertainties in calibrating the spatial distributions of galaxy clusters on dark energy constraints. In addition, we explore how the formation history of galaxy clusters impacts the self-calibration of cluster mass. In addition, we use N-body simulations to develop a new statistical sample of cluster-size halos in order to further understand the observable--mass distribution. We study the completeness of subhalos in our cluster sample by comparing them with the satellite galaxies in the Sloan Digital Sky Survey. We also study how subhalo selections impact the inferred correlation between formation time and optical mass tracers, including cluster richness and velocity dispersion.

The Local Group and Its Dwarf Galaxy Members in the Standard Model of Cosmology

Author : Azadeh Fattahi
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (119 download)

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Book Synopsis The Local Group and Its Dwarf Galaxy Members in the Standard Model of Cosmology by : Azadeh Fattahi

Download or read book The Local Group and Its Dwarf Galaxy Members in the Standard Model of Cosmology written by Azadeh Fattahi and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: According to the current cosmological paradigm, ``Lambda Cold Dark Matter'' (LambdaCDM), only ~20% of the gravitating matter in the universe is made up of ordinary (i.e. baryonic) matter, while the rest consists of invisible dark matter (DM) particles, which existence can be inferred from their gravitational influence on baryonic matter and light. Despite the large success of the LambdaCDM model in explaining the large scale structure of the Universe and the conditions of the early Universe, there has been debate on whether this model can fully explain the observations of low mass (dwarf) galaxies. The Local Group (LG), which hosts most of the known dwarf galaxies, is a unique laboratory to test the predictions of the LambdaCDM model on small scales. I analyze the kinematics of LG members, including the Milky~Way-Andromeda (MW-M31) pair and dwarf galaxies, in order to constrain the mass of the LG. I construct samples of LG analogs from large cosmological N-body simulations, according to the following kinematics constraints: (a) the separation and relative velocity of the MW-M31 pair; (b) the receding velocity of dwarf galaxies in the outskirts of the LG. I find that these constraints yield a median total mass of 2*10^#x12; solar masses for the MW and M31, but with a large uncertainty. Based on the mass and the kinematics constraints, I select twelve LG candidates for the APOSTLE simulations project. The APOSTLE project consists of high-resolution cosmological hydrodynamical simulations of the LG candidates, using the EAGLE galaxy formation model. I show that dwarf satellites of MW and M31 analogs in APOSTLE are in good agreement with observations, in terms of number, luminosity and kinematics. There have been tensions between the observed masses of LG dwarf spheroidals and the predictions of N-body simulations within the LambdaCDM framework; simulations tend to over-predict the mass of dwarfs. This problem is known as the ``too-big-to-fail'' problem. I find that the enclosed mass within the half-light radii of Galactic classical dwarf spheroidals, is in excellent agreement with the simulated satellites in APOSTLE, and that there is no too-big-to-fail problem in APOSTLE simulations. A few factors contribute in solving the problem: (a) the mass of haloes in hydrodynamical simulations are lower compared to their N-body counterparts; (b) stellar mass-halo mass relation in APOSTLE is different than the ones used to argue for the too-big-to-fail problem; (c) number of massive satellites correlates with the virial mass of the host, i.e. MW analogs with virial masses above ~ 3*10^#x12; solar masses would have faced too-big-to-fail problems; (d) uncertainties in observations were underestimated in previous works. Stellar mass-halo mass relation in APOSTLE predicts that all isolated dwarf galaxies should live in haloes with maximum circular velocity (V_max) above 20 km/s. Satellite galaxies, however, can inhabit lower mass haloes due to tidal stripping which removes mass from the inner regions of satellites as they orbit their hosts. I examine all satellites of the MW and M31, and find that many of them live in haloes less massive than V_max=20 km/s. I additionally show that the low mass population is following a different trend in stellar mass-size relation compared to the rest of the satellites or field dwarfs. I use stellar mass-halo mass relation of APOSTLE field galaxies, along with tidal stripping trajectories derived in Penarrubia et al., in order to predict the properties of the progenitors of the LG satellites. According to this prediction, some satellites have lost a significant amount of dark matter as well as stellar mass. Cra~II, And~XIX, XXI, and XXV have lost 99 per-cent of their stellar mass in the past. I show that the mass discrepancy-acceleration relation of dwarf galaxies in the LG is at odds with MOdified Newtonian Dynamics (MOND) predictions, whereas tidal stripping can explain the observations very well. I compare observed velocity dispersion of LG satellites with the predicted values by MOND. The observations and MOND predictions are inconsistent, in particular in the regime of ultra faint dwarf galaxies.

Dark Matter And Cosmic Web Story (Second Edition)

Author : Jaan Einasto
Publisher : World Scientific
ISBN 13 : 9811292159
Total Pages : 412 pages
Book Rating : 4.8/5 (112 download)

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Book Synopsis Dark Matter And Cosmic Web Story (Second Edition) by : Jaan Einasto

Download or read book Dark Matter And Cosmic Web Story (Second Edition) written by Jaan Einasto and published by World Scientific. This book was released on 2024-04-29 with total page 412 pages. Available in PDF, EPUB and Kindle. Book excerpt: The concepts of dark matter and the cosmic web are some of the most significant developments in cosmology in the past century. They have decisively changed the classical cosmological paradigm, which was first elaborated upon during the first half of the 20th century but ran into serious problems in the second half. Today, they are integral parts of modern cosmology, which explains everything from the Big Bang to inflation to the large-scale structure of the Universe.Dark Matter and Cosmic Web Story describes the contributions that led to a paradigm shift from the Eastern point of view. It describes the problems with the classical view, the attempts to solve them, the difficulties encountered by those solutions, and the conferences where the merits of the new concepts were debated. Amidst the science, the story of scientific work in a small country occupied by the Soviet Union and the tumultuous events that led to its breakup are detailed as well.The development of cosmology has often treated as a West-East conflict between the American school led by Jim Peebles in Princeton and the Soviet team led by Yakov Zeldovich in Moscow. Actually, the development of ideas was broader, and a certain role played the Tartu team. The Tartu cosmology school was founded by Ernst Öpik and has its own traditions and attitude to science. In the new edition of the book the interplay between three cosmology schools is written in more detail. The recent development of dark matter and cosmic web studies is described, as well as the evolution of global properties of the cosmic web.This book is accompanied by a website which contains additional material: copies of the originals of some crucial papers, astronomical movies, and movies which showcase the private life of the author. In this second edition, two chapters on the statistical description of the cosmic web and its development were added, as well as chapter on the sociology of science. To keep the length of this book reasonable, a lot of reorganisation of the text has been done as well.

Probing Local Group Galactic Substructure with Cosmological Simulations

Author : Gregory Alan Dooley
Publisher :
ISBN 13 :
Total Pages : 358 pages
Book Rating : 4.:/5 (1 download)

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Book Synopsis Probing Local Group Galactic Substructure with Cosmological Simulations by : Gregory Alan Dooley

Download or read book Probing Local Group Galactic Substructure with Cosmological Simulations written by Gregory Alan Dooley and published by . This book was released on 2017 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Lambda cold dark matter (ACDM) model is enormously successful at predicting large scale structure in the Universe. However, some tensions still remain on small scales, specifically regarding observed satellites of the Milky Way (MW) and Andromeda. Foremost among the problems have been the missing satellite, too big to fail, and cusp/core problems, which concern the expected abundance of satellites and their inner structure. This Ph.D. thesis consists of a series of studies using dark matter only cosmological N-body simulations of MW-mass galaxies to address topics related to these issues. In light of the recent Planck mission, I investigate how changes to cosmological parameters affect dark matter halo substructure. I find that the process of continuous sub-halo accretion and destruction leads to a steady state description of most subhalo properties in a given host, unchanged by small fluctuations in cosmological parameters. Subhalo concentration, maximum circular velocity, and formation times, however, are somewhat affected. One way to reduce the central density of satellites, as needed to solve the cusp/core and too big to fail problems, is through self-interacting dark matter (SIDM). I search for new implications of SIDM and find that stars in satellites spread out to larger radii and are tidally stripped at a higher rate in SIDM than CDM, even though the mass loss rate of dark matter is unchanged. These signatures should be particularly prominent in ultrafaint dwarf galaxies for the class of otherwise difficult to constrain velocity-dependent SIDM models. I also helped carry out the Caterpillar project, a suite of 36 high mass resolution (~ 10' Mo/particle) simulations of MW-like galaxies used to study diversity in halo substructure. To these, I apply abundance matching and reionization models to make novel predictions about the abundance of satellites in isolated dwarf galaxies out to 8 Mpc to help guide future searches. Applying the same techniques to predict satellites within 50 kpc of the LMC, I discover large discrepancies with the observed stellar mass function, which may lead to new constraints on the galaxy stellar mass-halo mass relationship, and the ability of reionization to leave dark matter halos entirely dark.

Dark Matter in Dwarf Spheroidal Galaxies

Author :
Publisher :
ISBN 13 :
Total Pages : 288 pages
Book Rating : 4.:/5 (918 download)

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Book Synopsis Dark Matter in Dwarf Spheroidal Galaxies by :

Download or read book Dark Matter in Dwarf Spheroidal Galaxies written by and published by . This book was released on 2014 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt: From their unique location in orbit around the Milky Way, dwarf spheroidal galaxies are excellent laboratories for studying dark matter. In this thesis, information from the dynamics of stars in dwarf spheroidal galaxies is used to infer the mass distribution of dark matter in these objects. A more precise measurement of the mass distribution would give us valuable clues about the nature of dark matter and can help us to target dark matter searches. Classically, the mass of a dwarf galaxy is estimated from measurements of the stellar velocity dispersion profile which tells us the width of the stellar velocity distribution at different distances from the galactic centre. Unfortunately, the velocity dispersion profile only constrains the mass of the galaxy at one radius and places little constraint on dark matter models. To improve upon the classic analysis, one can complement information from the velocity dispersion measurements (the second moment of the velocity distribution) with information from higher moments which constrain the shape of the velocity distribution. We relax assumptions made in previous works and develop new methods that for the first time allow us to draw robust conclusions about the ability of higher moments to differentiate between dark matter models that are indistinguishable in the classic analysis. Whilst our methods are not able to verify predictions from cosmological simulations of dark matter, we found that the fourth moment of the velocity distribution can dramatically improve constraints on the mass distribution of dwarf galaxies and can be used to improve the precision of dark matter detection experiments.

Dark Sky, Dark Matter

Author : J.M Overduin
Publisher : CRC Press
ISBN 13 : 1420034510
Total Pages : 216 pages
Book Rating : 4.4/5 (2 download)

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Book Synopsis Dark Sky, Dark Matter by : J.M Overduin

Download or read book Dark Sky, Dark Matter written by J.M Overduin and published by CRC Press. This book was released on 2002-09-01 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt: Olbers' paradox states that given the Universe is unbounded, governed by the standard laws of physics, and populated by light sources, the night sky should be ablaze with light. Obviously this is not so. However, the paradox does not lie in nature but in our understanding of physics. A Universe with a finite age, such as follows from big-bang theor

The Mass Distribution and Assembly of the Milky Way from the Properties of the Magellanic Clouds

Author :
Publisher :
ISBN 13 :
Total Pages : 9 pages
Book Rating : 4.:/5 (16 download)

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Book Synopsis The Mass Distribution and Assembly of the Milky Way from the Properties of the Magellanic Clouds by :

Download or read book The Mass Distribution and Assembly of the Milky Way from the Properties of the Magellanic Clouds written by and published by . This book was released on 2012 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present a new measurement of the mass of the Milky Way (MW) based on observed properties of its largest satellite galaxies, the Magellanic Clouds (MCs), and an assumed prior of a?CDM universe. The large, high-resolution Bolshoi cosmological simulation of this universe provides a means to statistically sample the dynamical properties of bright satellite galaxies in a large population of dark matter halos. The observed properties of the MCs, including their circular velocity, distance from the center of the MW, and velocity within the MW halo, are used to evaluate the likelihood that a given halo would have each or all of these properties; the posterior probability distribution function (PDF) for any property of the MW system can thus be constructed. This method provides a constraint on the MW virial mass, 1.2{sup +0.7} - {sub 0.4}(stat.){sup +0.3} - {sub 0.3}(sys.) x 1012 M {circle_dot} (68% confidence), which is consistent with recent determinations that involve very different assumptions. In addition, we calculate the posterior PDF for the density profile of the MW and its satellite accretion history. Although typical satellites of 1012 M {circle_dot} halos are accreted over a wide range of epochs over the last 10 Gyr, we find a ≈72% probability that the MCs were accreted within the last Gyr, and a 50% probability that they were accreted together.

The Search for WIMP Dark Matter Continuum Gamma-ray Emission from Dark Matter Satellites in the Milky Way Using the Fermi LAT

Author : Wang Ping
Publisher : Stanford University
ISBN 13 :
Total Pages : 167 pages
Book Rating : 4.F/5 ( download)

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Book Synopsis The Search for WIMP Dark Matter Continuum Gamma-ray Emission from Dark Matter Satellites in the Milky Way Using the Fermi LAT by : Wang Ping

Download or read book The Search for WIMP Dark Matter Continuum Gamma-ray Emission from Dark Matter Satellites in the Milky Way Using the Fermi LAT written by Wang Ping and published by Stanford University. This book was released on 2011 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on the search for unknown dark matter (DM) satellites in the Milky Way using the Fermi Large Area Space Telescope (LAT). The Fermi Gamma-ray Space Telescope (Fermi) is a next generation space observatory, which was successfully launched on June 11th, 2008. The LAT is the principal scientific instrument onboard. Its unprecedented angular resolution and sensitivity in the 100 MeV to > 300 GeV energy range makes it an excellent instrument for probing the sky for DM satellites. Current N-body simulations based on the Lambda-CDM cosmology model predict a large number of as yet unobserved DM satellites in our galaxy; some satellites are predicted to be extended sources (> 1deg extension) as seen by the LAT. Our work assumes that a significant component of DM is a Weakly Interacting Massive Particle (WIMP) in the 100 GeV mass range. The annihilation of WIMPs results in many high energy gamma rays that can be well measured by the LAT. The WIMP produced gamma-ray spectrum from the putative DM satellites is considerably harder than most astrophysical sources. Also, DM satellites have no astronomical counterparts in the X-ray and radio bands, and the emission has no time variability. My thesis will focus on a blind analysis in the search for unknown DM satellites using one year of LAT data, and setting constraints on some WIMP models based on the results of our analysis in which we find no candidates.

Particle Dark Matter

Author : Gianfranco Bertone
Publisher : Cambridge University Press
ISBN 13 : 0521763681
Total Pages : 763 pages
Book Rating : 4.5/5 (217 download)

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Book Synopsis Particle Dark Matter by : Gianfranco Bertone

Download or read book Particle Dark Matter written by Gianfranco Bertone and published by Cambridge University Press. This book was released on 2010-01-07 with total page 763 pages. Available in PDF, EPUB and Kindle. Book excerpt: Describes the dark matter problem in particle physics, astrophysics and cosmology for graduate students and researchers.

Informing Dark Matter Detection Experiments Using Cosmological Simulations of Milky Way-like Galaxies

Author : R. Poole-McKenzie
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (129 download)

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Book Synopsis Informing Dark Matter Detection Experiments Using Cosmological Simulations of Milky Way-like Galaxies by : R. Poole-McKenzie

Download or read book Informing Dark Matter Detection Experiments Using Cosmological Simulations of Milky Way-like Galaxies written by R. Poole-McKenzie and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

The Milky Way's Dwarf Satellite Galaxies in [L]CDM

Author : Christopher Barber
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (119 download)

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Book Synopsis The Milky Way's Dwarf Satellite Galaxies in [L]CDM by : Christopher Barber

Download or read book The Milky Way's Dwarf Satellite Galaxies in [L]CDM written by Christopher Barber and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Current models of cosmology and galaxy formation are possibly at odds with observations of small-scale galaxies. Such is the case for the dwarf spheroidal (dSph) galaxies of the Milky Way (MW), where tension exists in explaining their observed abundance, mass, and internal structure. Here we present an analysis of the substructure surrounding MW-sized haloes in a Lambda Cold Dark Matter (LCDM) simulation suite. Combined with a semi-analytic model of galaxy formation and evolution, we identify substructures that are expected to host dSph galaxies similar to the satellites of the MW. We subsequently use these simulations to investigate the orbital properties of dSph satellite galaxies to make contact with those orbiting the MW. After accretion into the main halo, the higher mass ``luminous'' substructure remains on highly radial orbits while the orbits of lower mass substructure, which are not expected to host stars, tend to scatter off of the luminous substructure, and thus circularize over time. The orbital ellipticity distribution of the luminous substructure shows little dependence on the mass or formation history of the main halo, making this distribution a robust prediction of LCDM. Through comparison with the ellipticity distribution computed from the positions and velocities of the nine MW dSph galaxies that currently have proper motion estimates as a function of the assumed MW mass, we present a novel means of estimating the virial mass of the Milky Way. The best match is obtained assuming a mass of 1.1 x 10^12 M_sun with 95 per cent confidence limits of (0.6 - 3.1) x 10^12 M_sun. The uncertainty in this estimate is dominated by the large uncertainties in the proper motions and small number of MW satellites used, and will improve significantly with better proper motion measurements from Gaia. We also measure the shape of the gravitational potential of subhaloes likely to host dSphs, down to radii comparable to the half-light radii of MW dSphs. Field haloes are triaxial in general, while satellite haloes become more spherical over time due to tidal interactions with the host. Thus through the determination of the shape of a MW dSph's gravitational potential via line of sight velocity measurements, one could in principle deduce the impact of past tidal interactions with the MW, and thus determine its dynamical history. Additionally, luminous subhaloes experience a radial alignment of their major axes with the direction to the host halo over time, caused by tidal torquing with the host's gravitational potential during close pericentric passages. This effect is seen at all radii, even down to the half-light radii of the satellites. Radial alignment must be taken into account when calibrating weak-lensing surveys which often assume isotropic orientations of satellite galaxies surrounding host galaxies and clusters.

Community, Competition and Citizen Science

Author : Asst Prof Anne Holohan
Publisher : Ashgate Publishing, Ltd.
ISBN 13 : 9781409452980
Total Pages : 150 pages
Book Rating : 4.4/5 (529 download)

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Book Synopsis Community, Competition and Citizen Science by : Asst Prof Anne Holohan

Download or read book Community, Competition and Citizen Science written by Asst Prof Anne Holohan and published by Ashgate Publishing, Ltd.. This book was released on 2013-12-06 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt: Drawing on face-to-face and online ethnographic, survey and interview data with participants in distributed computing projects around the world, this book sheds light on the organizational and social structures of voluntary distributed computing projects, communities and teams, with close attention to questions of motivation in projects that offer little or no traditional forms of reward, either financially or in terms of participants' careers. With its focus on non-market, non-hierarchical cooperation, this book is a case study of networked individuals around the world who are part of a new social production of information.

Gas Accretion onto Galaxies

Author : Andrew Fox
Publisher : Springer
ISBN 13 : 3319525123
Total Pages : 386 pages
Book Rating : 4.3/5 (195 download)

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Book Synopsis Gas Accretion onto Galaxies by : Andrew Fox

Download or read book Gas Accretion onto Galaxies written by Andrew Fox and published by Springer. This book was released on 2017-03-23 with total page 386 pages. Available in PDF, EPUB and Kindle. Book excerpt: This edited volume presents the current state of gas accretion studies from both observational and theoretical perspectives, and charts our progress towards answering the fundamental yet elusive question of how galaxies get their gas. Understanding how galaxies form and evolve has been a central focus in astronomy for over a century. These studies have accelerated in the new millennium, driven by two key advances: the establishment of a firm concordance cosmological model that provides the backbone on which galaxies form and grow, and the recognition that galaxies grow not in isolation but within a “cosmic ecosystem” that includes the vast reservoir of gas filling intergalactic space. This latter aspect in which galaxies continually exchange matter with the intergalactic medium via inflows and outflows has been dubbed the “baryon cycle”. The topic of this book is directly related to the baryon cycle, in particular its least well constrained aspect, namely gas accretion. Accretion is a rare area of astrophysics in which the basic theoretical predictions are established, but the observations have been as yet unable to verify the expectations. Accretion has long been seen around the Milky Way in so-called High Velocity Clouds, but detecting accretion even around nearby galaxies has proved challenging; its multi-phase nature requires sensitive observations across the electromagnetic spectrum for full characterization. A promising approach involves looking for kinematic signatures, but accretion signatures are often confused with internal motions within galaxies. Accretion studies therefore touch a wide range of astrophysical processes, and hence a wide cross-section of the astronomical community. As observational facilities are finally able to access the wavelength ranges and depths at which accretion processes may be manifest, the time is right to survey these multiple lines of investigation and determine the state of the field in accretion studies of the baryon cycle.